What is adaptive servo-ventilation (ASV)?

-ASV is an exciting breakthrough created by the ResMed Company specifically for the treatment of central as well as obstructive apneas.

How does ASV work?

-ASV is a new form of positive airway pressure unit that continuously monitors the patient's breathing pattern in exquisite detail.

-Whenever it detects significant reductions or pauses in breathing, it intervenes with just enough support to maintain the patient's breathing at 90% of what had been normal for that individual just prior to the decrease in breathing.

-Then, when the patient's breathing problem ends, the machine "backs out" gently.

-Also, when the patient's breathing is stable, ASV provides just enough pressure support to help maintain airway patency: thereby providing an approximate 50% reduction in the work of breathing.

The machine is subtle in its interventions...and it continuously adjusts itself to meet the patient's needs in a manner that will feel normal for that patient at that point in time: which renders it comfortable.

ASV is the ultimate "smart machine".

How does ASV differ from the positive airway pressure machines that we already had available?

-Until the development of ASV, we had only three basic types of positive airway pressure (PAP) machines:

• CPAP (Continuous Positive Airway Pressure): a simple "blower" that delivers the same pre-set pressure continuously.
  
• Bilevel PAP: a machine that senses when the patient is beginning to exhale and responds by dropping the delivered pressure transiently to render exhalation easier.
  
• Bilevel PAP with intermittent mandatory ventilation (IMV): a bilevel unit that also senses when the patient stopped breathing--then responding by delivery of bursts of air at pre-set pressures and a pre-set rate to try to stimulate breathing. Its greatest disadvantage was that it would force the patient to try to adapt to the machine rather than the machine adapting to the patient's rate and depth of breathing. Many patients complain that they are unable to synchronize their breathing with these machines. Also, the abruptness with which these units deliver IMV can trigger arousals which in turn can precipitate more central apneas.

-ASV is unique in that it continuously adapts to the patient. It provides just enough support when the patient needs it...in a manner so similar to the patient's own recent breathing pattern and rate that it is not only comfortable, but also, it is unlikely to provoke arousals and more central apneas.

Which patients with central sleep apneas are most likely to benefit from ASV?

-Patients with complex sleep apnea (central apneas emerging with use of CPAP or bilevel PAP).

-Patients with heart failure or atrial fibrillation who have central sleep apnea - with or without obstructive sleep apneas.

How much more effective is ASV in these patients, when compared to the alternatives?

-A study compared the effectiveness of ASV, CPAP, bilevel PAP with IMV and oxygen in patients with heart failure. Here are the results:

*Teschler H et. al. Adaptive Pressure Support Servo-Ventilation. A Novel Treatment for Cheyne-Stokes Respiration in Heart Failure. Am J Resp & Crit Care Med 16: 614-619, 2001

-Only ASV reduced the number of episodes of apnea and hypopnea to normal, and ASV clearly was superior at reducing sleep fragmentation and increasing vital stages of sleep needed for proper rest. All patients preferred ASV to CPAP.

Since ASV adjusts to the patient, are titration sleep center overnight recordings needed before treatment with ASV is prescribed?

-Yes, for two important reasons:

• There are three parameters of ASV that must be adjusted to the individual patient's needs: the end-expiratory pressure and both the minimal and maximal pressure support settings. As with positive airway pressure in general, these devices must be set just right for the patient or the end result will be much like buying the wrong size shoes. We believe strongly in precise titrations, since problems with positive airway pressure treatment are similar to a piece of gravel on one's shoes: the size of the piece of gravel doesn't matter. If everything is not just right, the patient will be likely to abandon treatment.
  
• Insurance companies typically require proof that a treatment is effective before they will pay for it.

-Therefore, if you or a loved one suffers from indications of central sleep apneas--whether from use of CPAP/bilevel PAP for obstructive sleep apnea or as a complication of heart disease, it is important when you select a sleep center for care that you first ensure that the center has ASV machines on site for use during overnight monitoring and that the center's technologists have been properly trained in use of these devices.

Do many sleep centers offer ASV titrations to their patients at this point in time?

-No, for two reasons. First, ASV became available in the United States only recently, and Medicare coverage for this treatment was just granted in April 2006. The latter is very important because most insurance companies now follow Medicare rules when determining what tests and treatments for which they will grant coverage.

-A second problem is that for unclear reasons, a large number of established sleep centers do not attempt to treat central apneas at all: they still do not even offer trials of bilevel PAP with IMV for central apneas despite the fact that the latter have been available in the US since 1990. These centers simply focus on obstructive apneas and routinely prescribe only CPAP or straight bilevel (without IMV) machines. It is difficult to understand why they ignore central apneas, since they complicate positive airway treatment of obstructive apneas in 15-20% of cases and can cause severe sleep fragmentation to the point that patients simply abandon treatement.

-As of late September, 2006, the Columbus Community Health Regional Sleep Disorders Center is the only sleep center in central Ohio with ASV units on site.

What has been the experience with use of ASV at the Columbus Community Health Regional Sleep Disorders Center?

-Overwhelmingly positive. We obtained our first ResMed VPAP Adapt SV in late July, 2006 and have found this treatment so invaluable that we added a second machine in September. As of mid-September, we have already used the device in thirteen patients and prescribed it for home use in twelve patients (the thirteenth slept more soundly during a second overnight study and could be treated with straight CPAP.

-ASV has worked perfectly in all of these patients, normalizing breathing and oxygen levels in all of them while improving sleep quality. It eliminated the need for supplemental oxygen in every case. Several of these patients previously had been struggling to use bilevel PAP with IMV, plus supplemental oxygen, plus sleeping in a sitting position and were doing poorly. They now are sleeping soundly.

-Our ASV experience was summarized in a recent press release, reproduced here:

Click here for more information on how adaptive servo-ventilation eliminates central sleep apneas.